Mail cannot save information about your mailboxes because there isn't enough space in your home folder

I have a 2012 21 iMac with FusionDrive. I replaced the HDD with a 2 TB SSD. When I upgraded to Catalina I experienced the same issues as everyone else. I reinstalled Catalina from scratch but did not work until I saw re5i5tor’s post on this feed and follows the same steps (less bootable USB as you can get the OS online vie the EFI) but basically rebuilt the Fusion and now my machine works as intended with all the issues fixed. I even formatted the drive to APFS - since I had an all SSD disk. For a 8 year old machine it actually works well. I had posted 4 times now to confirm that the solution re5i5tor gave works. Hope it helps.

I "resolved" the issue by using Spark instead of Mail. However the Mac ist still failing from time to time and get's really slow. Hope desperately for another update.

iMac 5K 2017 with Fusion Drive (750 GB SSD + 4 TB HDD) having 200 GB free space, 32 GB RAM.

Fusion Drive was previously used on an iMac 2011, was HFS+ before being converted to APFS with the Mojave install one year ago.

I have the feeling this is a Fusion Drive / APFS related issue.

As suggested (NikkolaPD Nov 12) here are more details of my iMac installationin

My iMac is 

iMac (27 inch, Late 2013)

MacOS Catalina 10.15.1 

Processor 3,5 GHz Quad-Core Intel Core i7

Memory 8 GB 1600 MHz DDR 

Startup disk Fusion disk consisting of 480GB SSD, 120GB Flash.    APFS formatted.

The original Fusion disk (rotating + flash) was substituted for SSD+Flash fusion by Humac Danmark (Apple Danmark) a couple of years ago.  

It was running High Sierra up to a couple of weeks ago. I had to clean install Catalina in order to upgrade.  

Catalina 10.15.1 was clean installed on the fusion disk via a bootable USB stick.

(Bootable USB stick created, Boot from USB stick, Erase and reformat with APFS the Macintosh HD volume, rebuild as Fusion volume, Migration assistant to restore sw from a Time machine backup). (see https://discussions.apple.com/thread/8551587 )

I tried the fix posted by clivesey 10th Oct 2019 1:03AM but still have the same mail problem. I have also tried clearing out all my mails in all my accounts (iCloud mail; gmail, hotmail) and applying the fix again. Still same problem. I have lots of space on my mac ( 64GB available of a 600GB SSD/flash 'fusion' drive) and am using iCloud storage where I also have tons of available space (1,8TB available!). Hope there comes a Catalina fix soon addressing this problem.

Hi all,

After I first posted, things went from bad to worse. Mail disk space errors, out of memory errors, iCloud calendar lost all its data, unfixable fusion drive errors..., loss of recovery partition, unable to safe boot....

Had to erase, repartition, reinstall Catalina 10.15.1 from USB, reinstall from a carbon copy cloner backup.

2 weeks of inconvenience, 48 hours of downtime, not impressed by this OS iteration.

Here are my specs below. Also a fusion drive.

 Model Name: iMac

  Model Identifier: iMac17,1

  Processor Name: Quad-Core Intel Core i7

  Processor Speed: 4 GHz

  Number of Processors: 1

  Total Number of Cores: 4

  L2 Cache (per Core): 256 KB

  L3 Cache: 8 MB

  Hyper-Threading Technology: Enabled

  Memory: 16 GB

  Boot ROM Version: 173.0.0.0.0

  SMC Version (system): 2.34f3

So far then, it appears that everyone with the problem is running a Fusion drive. And that the problem is not limited to Mail app only.

So to state the Captain Obvious conclusion, it appears this is not mail, but Catalina not correctly supporting / corrupting Fusion drives. Probably some subset of Fusion drives because it appears to be working for some on Fusion drives.

My specific case is that my iMac had a factory SSD + HD setup, then the HD failed and was replaced by a SATA SSD, but that was set up as a Fusion drive with the original SSD.

It is possible that the migration assistant step is where the Fusion drive is getting (re-)corrupted.

I have followed the steps in the diskutil resetfusion sequence and am in the process of setting up my iMac as a new machine. I’ll manually migrate my old local drive mailbox files.

I will report back on my results, though it will probably be a fairly long process (I’ve been living without the iMac since the problem occurred).

Everything is working here still.

I believe that a key part of the so-far-successful process is the “diskutil resetfusion” (and to avoid using Migration Assistant).

“diskutil resetfusion” is NOT the same as "blowing everything away on the HDD" aka reformatting. “diskutil resetfusion” breaks apart and reestablishes the Fusion drive.

I upgraded to Catalina prior to starting the project, and got my hands tied by this issue in the middle of it. It was not only Mail.app failing to operate, it was the whole iMac being unable to handle any serious workflow. And since I did not have the time to take any additional risks I just split the fusion drive and went full ahead with SSD + HDD as separate devices. Actually the iMac runs faster now!

The article you reference states at the beginning of the article: If your Fusion Drive appears as two drives instead of one in the Finder, it's no longer working as a Fusion Drive. Here's how to fix it....

My fusion drive appears as one drive on my iMac, therefore I do not see this as a logical solution. As I said, you need to provide additional statements to buttress your argument that I need to reformat my hard drive to due an issue associated with the email app.

Firstly if there is an Apple support article I don't need to buttress anything as it trumps all argument.

Secondly I didn't say it was the solution to a Mail problem, I said it is *the* solution to a split fusion drive where the small SSD part cannot hold all your ~/Library without filling up.

I went back to Mojave.

I had at least 2 days of extreme frustration trying to solve this problem; everything that could go wrong went wrong. I tried the 'Fusion Drive fix' and it did not work, I have a fusion drive but they are both SSD as I got an upgrade trying to get this iMac lemon to function better (and yes an authorised dealer installed it).

Getting Mojave back onto the computer was also a real pain but I finally did it, of course Time Capsule then refused to let me reinstall stuff, so I had to reconfigure just about everything.

I am now over the the anger and frustration I felt, but I think my next computer will be a Mac derivative, I have used Macs since the mid 90s: I was in essence a fan-boy, deciding to stick with them when everyone said they were doomed. I am so over that now.

I have costed what 'bang you get for your buck' and paying 3-4 times more for something that is basically not upgradable is nuts. I hear that going this route can be complicated but having just spent more than 2 days trying to sort out the problem on a real Mac, I am not sure that is an issue anymore!

One thing I would add is that I am not sure it is worth fixing the fusion drive, it may be better to have 2 separate drives, the original in my system is only 25gb so not a big deal and you can use if for other things; there is no guarantee this problem won't happen again with a future update if you join them back together.

Maybe slightly off-topic but the all this grief came from that precious upgrade.

Yes - I did this - my mac was pretending I had a fusion drive even though it was two SSDs - super annoying - I did this diskutil resetfusion above and it worked like a charm

Presumably because backups go into your user library which must be in the "system drive" if you split them rather than resetting to Fusion

https://support.apple.com/en-gb/HT207584

I was finally just resolving a major problem with my iTunes Library in the Music App when my previously working Mail App threw me this error. I'm thinking I really should've waited on loading Catalina. Sigh.